The subject matter disclosed herein relates to a balance chamber defined by a poppet element of a valve and, more particularly, to a balance chamber defined by a poppet element of a high temperature valve.
Steam turbine control and stop valves often employ a balance chamber. During valve opening incidences, steam inside the balance chamber is evacuated through equalizer valves or poppet valves so that pressure inside the balance chamber is reduced and lesser hydraulic force is required to open the valve.
In order to ensure that a pressure inside the balance chamber is minimized, clearances between a valve disk and a wall of the balance chamber are often reduced as much as possible with seal rings used to provide high quality sealing characteristics. However, clearance reduction is limited since some predefined amount of clearance needs to be maintained in order to ensure that the valve opens and closes without jamming.
In certain applications, a balance chamber may be fixed to an upper head via bolts and, in some cases, the balance chamber material is different from the upper head material. The different materials have correspondingly different coefficients of thermal expansion (CTE) and, as such the upper head and the balance chamber expand at different rates when heat is generated (i.e., when the steam turbine starts up). At steady state, due to the difference in the CTEs, a bending stress is placed on the bolts and this bending stress is transmitted to the upper head via shear stress.